DC electric motors having a permanent magnet rotor, wound stator coils, a commutator and brushes are generally known as shown in Japanese patent publication JP4-200259. The motor disclosed in this patent publication employs a cylindrical commutator assembly that includes a pair of slip rings and a plurality of commutator bars extending axially from each slip ring. A first pair of brushes that are respectively connected to two poles of a DC power source make continuous sliding contact with the slip rings. A second pair of brushes that are connected to the stator coils, make sliding alternating contact with the commutator bars as the rotor turns. However, this kind of commutator makes the whole DC motor long in the axial direction.
U.S. Pat. No. 6,396,175 discloses a DC motor with a permanent magnet rotor and a commutator assembly having commutator segments and three slip rings, all arranged on a flat or planar surface. While such an assembly allows the motor to have a short axial length it requires a motor with a large radial dimension.
The present invention aims to provide a new DC motor having a permanent magnet rotor that can mitigate the above mentioned problem.